Fluorinated polymers are useful, for example, in the preparation of low surface energy and low refractive index coatings. In many cases, the fluorinated polymers have reactive groups such as alcohols that provide reactive sites for crosslinking reactions. Currently, such fluorinated polymers are generally prepared in commercial quantities using free-radical polymerization of corresponding fluorinated monomers. Such monomers are generally expensive and can be troublesome to obtain and/or handle. Further, in some cases it may be necessary to derivatize the resulting polymer in order to obtain the reactive groups.
One well-known industrial process for preparing fluorochemical compounds is the electrochemical fluorination process commercialized initially in the 1950's by the 3M Company. This process, often referred to as Simons fluorination or electrochemical fluorination (ECF), is a method by which electric current is passed through an electrolyte solution containing a mixture of liquid anhydrous hydrogen fluoride and an organic compound intended to be fluorinated (the “substrate”). Generally, the Simons process is practiced with a constant current passed through the electrolyte. The current passing through the electrolyte causes one or more of the hydrogens of the substrate to be replaced by fluorine.
ECF has been used to make perfluoroalkanoyl fluorides, which have been of commercial value as precursors to carboxylic acids, esters, and alcohols. In general, ECF offers many advantages including relatively low cost and simplicity. However, as a general rule in electrochemical fluorination, the higher the molecular weight of the compound to be fluorinated, the greater the occurrence of breaking of carbon-carbon bonds. For example, as the molecular weight of the precursor CnH2n+1COX (X═F or Cl) increases, the yields of CnF2n+1COF decrease, as described by Abe et al. in Chapter 1 of Preparation, Properties, and Industrial Applications of Organofluorine Compounds, R. E. Banks, ed., pages 24-28, Halsted Press, New York (1982). In that case, the yields were as follows: n=1 (71% yield), n=3 (36% yield), n=6 (16% yield), n=7 (10% yield), n=11 (0.5% yield), n=15 (0% yield). In part, these lower yields are due to cleavage of the carbonyl group to give CnF2n+1F; in part due to reaction between the alkyl chain and the carbonyl oxygen, leading to 5- and 6-membered ether rings for n=4 and higher.
Hence, electrochemical production of fluorine-containing compounds has typically been applied to relatively low molecular weight compounds.